Brake applying means



y 1 1939- F. cs. PARNELL I I 0 BRAKE APPLYING MEANS F'il ed Jan. s, 1938 3 Sheets-Sheet 1 y 11, 1939- F. G. PARNELL 2,165,760

BRAKE APPLYING MEANS Filed Jan. 8, 1938 3 Sheets-Sheet 2 ve/6 2221' zz/2,66, ja

y 11, 1939- F. G. PARNELL 2,165,750

BRAKE APPLYING MEANS Filed Jan. 8, 1938 3 Sheets-Sheet 3 3 77' /fi C:

if 3;; iii {5 1/ Jaw d 1% 7 77 if 5273 2) a 7% E e/Zia Zia/Mg Z Patented July 11, 1939 UNITED STATES PATENT OFFICE to Automotive Products Company London, England Limited,

Application January 8, 1938, Serial No. 184,064 In Great Britain January 11, 1937 4 Claims.

This invention relates to brake-applying means of the kind in which a shoe or shoes are moved into contact with the drum by mechanism comprising a pair of elongated link members arranged obliquely end to end and operatively connected with actuating means which move the two cooperating ends simultaneously in a transverse direction in the manner of a toggle, the outer extremities of the link members being thereby caused to have a spreading action and apply the brake.

The invention has for its object'to provide an improved construction of brake-applying means which is very simple to manufacture and which has been found to possess a very good operating efiiciency, the friction losses being comparatively small. The invention is accordingly.characterised by the fact that the link members in a brakeapplying device of the kind above referred to abut end to end and roll one against the other during the application of the brake.

Thus, the invention provides a brake-applying means of the above kind in which each of the link members has a curved surface at each end, the arrangement being such that one of said surfaces rolls upon the other link member during the application of the brake, and the other curved surface of the first-mentioned link member simultaneously rolls upon the end of the brake shoe or an intermediate member adapted to actuate a shoe. Preferably the cooperating rolling surfaces on the link member and on the brake shoe or plunger are shaped so that a given movement of the actuating means produces a constant movement of the brake shoe or plunger throughout the whole range of movement of the applying means.

Two examples of brake-applying means according to the invention are illustrated in the accompanying drawings in which Figure 1 is a side elevation of a device adapted for mechanical and fluid pressure actuation;

. Figure 2 is a vertical longitudinal central section of Figure 1 with parts in elevation;

Figure 3 is a front elevation of a modified construction as arranged for mechanical actuation;

Figure 4 is a sectional plan taken on'the line 4-4 of Figure 3;

Figure 5 shows in plan view a modified form of link member arranged for use in the applying means in Figures 4 and 5; and

Figure 6 is a fragmentary diagrammatic side elevation showing to an enlarged scale a method of locating the link members.

A housing II] which is substantially T-shaped, as will be seen in Figure 2, is mounted upon the usual back-plate I l of the brake by means of studs l2 carrying nuts l3 and spring washers l4. It will be seen that the hole l5 in the back-plate is extended in a direction circumferentially of the brake so as to allow the housing Ill to float and take up its own position of equilibrium when the brake is applied. The transverse limb l6 of the housing I0 is formed throughout its length with a square channel H, the mouth of which is closed by a removable cover 18 secured by studs and nuts IS, SO as to form a passageway.

Two plunger members 26 and 2| are mounted slidably in the respective ends of the passageway I1, and each is grooved as indicated at 22 for engagement with the web portion of the corresponding brake shoe (not shown). The inner 1 parts of the plungers and 2| are formed with deep grooves 23 and 24 respectively which serve to accommodate a pair of fiat link members indicated at 25 and 26. At their outer ends these are formed each with a curved end surface 21 which is adapted to roll upon the bottom 28 of the corresponding groove 23 or 24. The outer end of each link member 25 and 26 has concentric side surfaces 29 which serve to locate the link member within the passage l1 and allow it to move angularly without creating undue side play.

At its inner end each of the link members 25 and 26 is also formed with a rounded surface indicated at 36, and these are adapted to roll together with a view to providing an extremely efiicient brake-applying action. For moving the link members 25 and 26 an actuating head 3| is arranged to move transversely across the centre part of the passageway 11, and is grooved at 32 for receiving the members 25 and 26. The latter are fitted respectively with pivot pins 33 and 34 which pass into the actuating head 3|, said head being notched as indicated at 35 for the accommodation of the pin 33 so as to ensure that any endwise thrust on the link members 25 and 26 is transmitted by them directly and is not imposed upon the pivot pins 33 and 34.

For moving the head 3| the latter is formed with a stem 36 which is screw-threaded at its outer end and carries a nut 31 and a bifurcated fitment 3B which is adapted to be connected mechanically with the usual hand brake lever (not shown), principally for the purpose of allowing the brake to be applied in emergency or during parking.

Liquid pressure is normally used for actuating the brake, and this is fed through a connection 39 into a cylinder 46 formed in that part of the housing passing through the back-plate II. A

collar 4| having a tubular stem 42 surrounding the stem 36 constitutes the fixed end wall of the working space, and is provided with a U-shaped annular cup 44 to prevent leakage of liquid. The cylinder 49 is also fitted with an annular piston 45 which has a U-shaped cup 46, and which bears at its outer end upon the nut 31 so that when liquid under pressure is forced into the cylinder 49 the stem 36 is moved so as to apply the brake. The return movement of the piston 45 and the actuating head 3! is effected by the usual pull off springs (not shown) associated with the brake shoes, a relatively weak coiled compression spring 41 within the cylinder 4|] serving merely to hold the packing cups 44 and 46 in position. Excessive movement of the piston 45 is prevented by a spring ring 48, while a flexible boot 49 serves to exclude water and grit in the usual manner. A bleeding plug 50 is provided at the highest part of the cylinder 40 for allowing air to be abstracted during the process of filling the system with working liquid.

It is, of course, well known to spread apart a pair of brake shoes by means of a simple toggle mechanism comprising for example a pair of links which are both connected by a pin joint to an actuating member, their outer ends being attached respectively also by pin joints to the shoes of the brake. This arrangement, however, is found to be unsatisfactory in practice as the mechanical advantage or leverage which is obtained varies considerably during the operative range of the parts. Moreover, the wholeof the circumferential braking force imparted by or to the shoes is imposed on the three pin.- joints, and has the effect of creating excessive friction as well as accelerating the wear of the moving parts. This defect is to all intents and purposes quite overcome by the invention, since the compression force exerted between the plunger members 20 and 2| is transferred by the relatively robust rolling surfaces 21 and 28 to the link members 25 and 26, and these in turn are in direct rolling contact at the curved surfaces 30. The only friction which is created upon the pins 33 and 34 is that due to the brake-applying tension in the stem 36. It will further be appreciated that the elongated nature of the link members 25 and 26 reduces the angular movement of the links relative to the applying head 3| to a very small amount, and this again considerably reduces the frictional loss.

In this embodiment the bottoms 28 of the grooves 23 and 24 are disposed truly radially with regard to the axis of the plungers 20 and 2|, and the curved surfaces 2! atthe outer ends of the link members are, therefore, shaped soas to produce a substantially uniform mechanical advantage throughout their range of movement. A close approximation which is satisfactory in practice can be obtained by making the surfaces 21 so that they are arcuate and are struck from the centre, which is indicated at 5| in Figure 2. In this figure the link members 25 and 26 occupy a position at the middle of their possible travel, and it will be seen that with this disposition of the parts the centre 5| lies upon the axis of the passageway H. The variation produced in the mechanical advantage is very slight, and this can, of course, be corrected by slightly modifying the shape of the curved surfaces 21. K

A modified construction of shoe-spreading device is shown in Figures 3 and 4. The back-plate carries a substantially T-shaped housing H), in the transverse limb l6 of which two slotted plunger members 20 and 2| are slidably mounted. At its outer end each of these plungers is formed with a depression 52, and these are engaged by thrust members 53 and 54 respectively cooperating with the web portions of the adjacent brake shoes indicated at 55 and 56. As will be more clearly seen in Figure 3 the thrust member 53 comprises a pair of screw-threaded parts, and this member can thus be extended in length by rotating an adjusting disc 51, thus regulating the working clearance of the brake shoes 55 and 56.

A stem 36 serves as the actuating means for the brake and is slidably mounted, the working parts being protected from moisture and dirt by a rubber boot 49. At its extremity the stem 36 is formed with a knob 58 which is seated in the base of a groove 32 formed in an actuating head 3| as before. The plungers 20 and 2| are also formed with grooves 23 and 24 respectively, and these accommodate a pair of link members indicated at 59 and 60. These are of the form shown in Figure 4, and are mounted within the actuating head 3! by a pair of loosely fitting pins 33 and 34 so that the adjacent curved surfaces 36 can roll upon one another and thus relieve the pins 33 and 34 from the main braking force. At their outer ends the link members 59 and 63 have curved surfaces 6| and 62 respectively which are concentric with the pins 33 and. 34 and which roll upon obliquely disposed cam surfaces 63 and constituting the bottoms of the grooves in the plungers 20 and 2|. Thus, as tension is applied to the stem 36 the inner ends of the link members 59 and 69 are drawn towards the backplate thus causing their outer end surfaces GI and 62 to roll upon the surfaces 63 and 64 and consequently spreading apart the brake shoes 55 and 55. As before, floating movement of the housing I0 can be permitted by providing clearance spaces in the back-plate as indicated at 65. A thin metal plate 66 conveniently serves to close the front end of the opening occupied by the actuating head, and a resilient finger 61 formed integrally with said plate cooperates with teeth on the periphery of the disc 5'! to preserve the as will be seen in Figure 5.

In the construction of brake-applying means illustrated in Figure 6, the link members have curved rolling surfaces 21 at their outer ends formed similarly to those in Figures 1 and 2, but

an alternative method is employed for locating the link members. As before, each link member 25 and 26 cooperates with a surface 28 upon a corresponding plunger member, such as that shown at 20, but these plunger members have a tooth 10 which mates with a corresponding space H formed in the link member. The link members are moved in the direction of the arrow 12 by an actuating head 3| which engages loosely with pivot pins 33 and 34 so that owing to the formation of the surfaces 21 the plunger members are spread apart. In the meantime the surface 13 of the tooth space H engages with the tooth 10, thus preventing the link members from slipping. By making the tooth 10 of involute form having its pitch line coincident with the surface 28, and by shaping the tooth space H correspondingly, a pure rolling action can be obtained between the tooth l0 and the surface 13 of the space N. This surface 13 is, of course, an involute and its curvature is obtained according to the usual method for gear teeth, taking the curved surface 2'! as the pitch line. Thus, with this form of link member there is rolling between the surfaces 36, the surfaces 21 and 28, and between the tooth l'!) and the surface '53 of the tooth space H the only rubbing friction occurring at pins 33 and 34 on account of the applying force.

What I claim is:

1. In a vehicle wheel brake, a toggle link mechanism for spreading apart a pair of brake shoes, comprising a housing, a pair of elongated thrust links within the housing arranged end to end, curved surfaces on the inner ends of the thrust links in contact with one another, actuating means extending through the housing which dis place the inner ends of the thrust links in a direction substantially at right angles to the direction of thrust, curved surfaces on the outer ends of the thrust links and a pair of plungers slidable within the housing, at opposite sides thereof, with which the curved outer end surfaces of the thrust links coact, the contact made at both ends of the links during the application of the brake being of a substantially wholly rolling nature.

2. In a vehicle wheel brake, a toggle link mechanism for actuating a pair of brake shoes, comprising a housing, a pair of elongated toggle links within the housing for applying thrust to spread apart the shoes, a curved surface on the inner end of each link, a curved surface on the outer end of each link concentric with the surface on the inner end, means extending through the housing for applying movement to the inner ends of the links in a direction at right angles to the direction of thrust, and a pair of plungers associated with the brake shoes and slidable Within the housing at opposite sides thereof, which plungers have inclined surfaces in contact with the curved outer ends of the links, the contact at both ends of the links being of a purely rolling nature.

3. In a vehicle wheel brake, toggle means for spreading a pair of brake shoes into contact with a brake drum, comprising a housing, a pair of elongated thrust links arranged end to end Within the housing, actuating means extending through the housing for moving the inner ends of the links in a direction at right angles to the direction of thrust, circular bearing bushes at the inner ends of the links and in contact with one another, curved surfaces at the outer ends of the link members, and intermediate plunger members slidable in the housing at opposite sides theref which transmit the thrust from the links to the brake shoes and have inclined bearing surfaces which make contact with the outer ends of the links, the action between the bushes at the inner ends of the links and between the outer ends of the links and the plunger members being of a wholly rolling nature during the application of the brake.

4. In a vehicle wheel brake, a toggle mechanism for spreading apart a pair of brake shoes into contact with a brake drum, comprising a housing, a pair of elongated thrust links arranged end to end within the housing, actuating means extending through the housing for moving the inner ends of the links in a direction substantially at right angles to the direction of thrust in the links, curved surfaces at the inner ends of the links in contact with one another, a toothed surface at the outer end of each link, a plunger member adjacent the outer end of each link and slidable within the housing to operate the brake shoes, and a toothed surface on the plunger member which ccacts with the toothed surface at the outer end of the corresponding link member, a wholly rolling action taking place at the ends of the link members when the brake shoes are being spread apart.

FRANK GORDON PARNELL. 

